Structural Diversity of Copper(I)-N-Heterocyclic Carbene Complexes; Ligand Tuning Facilitates Isolation of the First Structurally Characterised Copper(I)-NHC Containing a Copper(I)-Alkene Interaction

The preparation of a series of imidazolium salts bearing N-allyl substituents, and a range of substituents on the second nitrogen atom that have varying electronic and steric properties, is reported. The ligands have been coordinated to a copper(I) centre and the resulting copper(I)–NHC (NHC=N-heterocyclic carbene) complexes have been thoroughly examined, both in solution and in the solid-state. The solid-state structures are highly diverse and exhibit a range of unusual geometries and cuprophilic interactions. The first structurally characterised copper(I)–NHC complex containing a copper(I)–alkene interaction is reported. An N-pyridyl substituent, which forms a dative bond with the copper(I) centre, stabilises an interaction between the metal centre and the allyl substituent of a neighbouring ligand, to form a 1D coordination polymer. The stabilisation is attributed to the pyridyl substituent increasing the electron density at the copper(I) centre, and thus enhancing the metal(d)-to-alkene(π*) back-bonding. In addition, components other than charge transfer appear to have a role in copper(I)–alkene stabilisation because further increases in the Lewis basicity of the ligand disfavours copper(I)–alkene binding

A five-membered PdSbn coordination series

Five complexes of the general formula PdCl2(SbMe2Cl)n (n = 1-5) have been synthesised by combining [PdCl2(MeCN)2] and SbMe2Cl in different molar ratios in toluene. Their solid-state structures have been determined by X-ray crystallography. The complexes display considerable structural diversity: [Pd4Cl8(SbMe2Cl)4] (1, n = 1) is a chloride bridged tetramer, [Pd2Cl4(SbMe2Cl)4] (2, n = 2) is a dimer, [PdCl(SbMe2Cl)2(SbMe2Cl2)] (3, n = 3) is a supramolecular polymer, [Pd2(SbMe2Cl)8]Cl4¬ (4, n = 4) is a loosely associated dimer and [Pd(SbMe2Cl)5]Cl2 (5, n = 5) is a monomer with square pyramidal PdSb5 coordination geometry. Each structure contains secondary interactions between coordinated Sb centres and chloride ligands or anions, resulting in five-coordinate Sb in all cases with a range of Sb∙∙∙Cl bond lengths. The electronic structures of these complexes have been investigated using DFT methods including NBO and Pipek-Mezey localised orbital methods in order to interrogate both the Sb-Pd and secondary Sb∙∙∙Cl bonding

Silver(I) N-Heterocyclic Carbene Complexes Derived from Clotrimazole: Antiproliferative Activity and Interaction with an Artificial Membrane-Based Biosensor

With the aim of combining the potential anticancer properties of both clotrimazole, an imidazole based antifungal agent, and silver(I) N-heterocyclic carbenes, 13 novel silver(I) N-heterocyclic carbene complexes derived from clotrimazole were synthesized. The complexes were fully characterized, and the partition coefficient of each was determined to provide a measure of hydrophobicity. The antiproliferative properties of the complexes against cancerous and noncancerous cell lines found optimum cytotoxicity when the complex displays an “intermediate lipophilicity”, which describes a complex that possesses both water-soluble groups and lipophilic aromatic groups. The silver complexes were screened on a synthetic biomembrane-like device using a chip-based phospholipid-coated Pt/Hg electrode embedded in a flow cell system. The results are recorded as rapid cyclic voltammograms (RCVs), which give insight into the interactions of the complexes with a cell membrane. Interestingly the principle of “intermediate lipophilicity” also applies to the monolayer interaction to which the silver atom significantly implements an irreversibility

Mechanistic Elucidation of the Arylation of Non-Spectator N-Heterocyclic Carbenes at Copper using a Combined Experimental and Computational Approach

CuI(NHC)Br complexes (NHC = N-heterocyclic carbene) undergo a direct reaction with iodobenzene to give 2-arylated benzimidazolium products. The nature of the Nsubstituent on the NHC ligand influences the reactivity of the CuI(NHC)Br complex towards arylation. N-Benzyl or Nphenyl substituents facilitate arylation, whereas N-mesityl substituents hinder arylation. Density functional theory calculations show that an oxidative addition/reductive elimination pathway, involving CuIII species, is energetically feasible. A less hindered CuI(NHC)Br complex, with N-benzyl groups, is susceptible to oxidation reactions to give 1,3- dibenzylbenzimidazolium cations containing a CuIBrx anion (various polymorphs). The results described herein are of relevance to C-H functionalization of benz(azoles)